JP2012174565A - Raw material solution for forming oxide superconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a raw material solution to which a material for pinning is easily added even when an FF-MOD method is used, and which does not need treatment for thermally decomposing a metal complex and heat treatment for producing a compound for pinning, and can suitably control a size of particles for pinning.SOLUTION: The raw material solution for forming an oxide superconductor is used for forming an oxide superconductor of an RE123 system in which a pinning point of a magnetic flux is introduced on a substrate by using application thermal decomposition method. The raw material solution for forming the oxide superconductor is obtained by dispersing a predetermined amount of nanoparticles for forming the pinning point in a solution in which an organic metallic compound for forming the oxide superconductor is dissolved. A particle diameter of the nanoparticle is 5-100 nm. The organic metallic compound is an organic metallic compound which does not contain fluorine.

Description

  The present invention relates to a raw material solution for forming an oxide superconductor used when a layer made of an oxide superconductor is formed on a substrate using a coating pyrolysis method.

  Since the discovery of high-temperature superconductors that have superconductivity at the temperature of liquid nitrogen, development of high-temperature superconducting wires aimed at application to power devices such as cables, current limiters, and magnets has been actively conducted. In particular, an oxide superconducting thin film wire in which a thin film layer (oxide superconducting layer) made of an oxide superconductor is formed on a substrate has attracted attention.

  One method for producing such an oxide superconducting wire is a coating pyrolysis method (Metal Organic Deposition, abbreviated as MOD method) (Patent Document 1).

In this method, a raw material solution (MOD solution) produced by dissolving organometallic compounds of RE (rare earth element), Ba (barium), and Cu (copper) in a solvent was applied to a substrate to form a coating film. Thereafter, for example, a calcined heat treatment is performed at around 500 ° C., the organometallic compound is pyrolyzed, and the pyrolyzed organic component is removed to produce a calcined film that is a precursor of the oxide superconducting thin film. The calcined film is crystallized by subjecting it to a heat treatment at a higher temperature (for example, around 750 to 800 ° C.) to form a RE123-based superconducting thin layer represented by REBa ₂ Cu ₃ O _7-X to be oxidized. Compared with vapor phase methods (evaporation method, sputtering method, pulsed laser deposition method, etc.) that are mainly manufactured in vacuum, manufacturing facilities are simpler, and large areas and complicated Easy to adapt to various shapes Because it has the characteristics of constant and widely used.

  However, in recent years, there has been a strong demand for oxide superconducting thin film wires with improved critical current density Jc and critical current Ic. As a countermeasure, nano-sized quantized magnetic flux that penetrates RE123-based oxide superconductors under a magnetic field. In order to prevent the movement of the magnetic flux, artificially introducing a nano-sized magnetic flux pinning point (hereinafter referred to as “pin”) has been performed.

  Also in the MOD method described above, an oxide superconducting layer into which a pin is introduced is formed by adding an element that is a pin raw material, for example, a metal complex (salt) of Zr, to the raw material solution. (For example, Non-Patent Document 1).

JP 2007-165153 A

“Jc-B-θ characteristics of nanoparticle-introduced TFA-MODY1-xSmxBa2Cu3Oy (1-x, x, 2, 3, y are subscripts) wire”, Masashi Miura et al., TEION KOGKU (J. Cryo. Soc. Jpn. ) Vol. 44 no. 5 (2009) 210-216

  However, when the above method is used, in order to form a pin, a treatment for thermally decomposing the added metal complex and a heat treatment for generating a pin compound are required. In addition, in order for the generated pin compound to function sufficiently as a magnetic flux pin, it is necessary to agglomerate the generated pin compound so that it has a certain size or more. It is not easy to control.

  In addition, the above method has no problem when applied to the TFA-MOD method using an organometallic compound containing fluorine in the raw material solution, but in the case of the FF-MOD method using an organometallic compound not containing fluorine, It is difficult to properly control pin formation by adding a pin compound material in the form of a metal complex to the raw material solution, and it is difficult to perform orientational growth (epitaxial growth) in the process of crystal growth of an oxide superconductor. There was a problem in applying the above method.

  In view of the above problems, the present invention provides a raw material solution for the MOD method that can suitably control the particle size of a pin without requiring a treatment for thermally decomposing a metal complex or a heat treatment for generating a pin compound. The task is to do.

  As a result of various experiments and studies, the present inventor has found that the above problem can be solved by using a raw material solution to which nanoparticles are added.

  That is, when an oxide superconducting layer is formed by a MOD method using a raw material solution obtained by adding nanoparticles to a MOD solution, the nanoparticles function sufficiently as magnetic flux pins.

  Further, since the added nanoparticles are introduced as pins, there is no need for a separate treatment for thermally decomposing a metal complex or a heat treatment for generating a pin compound as in the prior art. In addition, since the particle size of the introduced pin follows the size of the added nanoparticle, the particle size of the pin can be easily and precisely controlled.

The present invention is based on the above knowledge, and the invention according to claim 1
A raw material solution for forming an oxide superconductor for forming an RE123-based oxide superconductor in which a magnetic flux pinning point is introduced on a substrate using a coating pyrolysis method,
A raw material for forming an oxide superconductor, wherein a predetermined amount of nanoparticles for forming the pinning point are dispersed in a solution in which an organometallic compound for forming the oxide superconductor is dissolved. It is a solution.

  By using the raw material solution for forming the oxide superconductor of this claim, as described above, it is possible to obtain an oxide superconducting layer in which nanoparticles functioning sufficiently as magnetic flux pins are appropriately controlled and introduced. An oxide superconducting thin film wire with improved Jc and Ic can be provided.

  “Nanoparticles for forming pinning points” function not only as nanoparticles that function as magnetic flux pins themselves but also as magnetic flux pins by reacting with organometallic compounds contained in the raw material solution during the main annealing process. Nanoparticles that produce pin compounds may also be used.

Examples of the former nanoparticles include Ag (silver), Au (gold), Pt (platinum), BaCeO ₃ (barium cerate), BaTiO ₃ (barium titanate), BaZrO ₃ (barium zirconate), and SrTiO _3. Examples thereof include nanoparticles such as (strontium titanate), and the material is not limited as long as the material does not adversely affect the superconducting properties of the oxide superconducting thin film.

  These nanoparticles are nanoparticles that do not react with the raw material solution. For this reason, a pin can be introduced without performing a separate heat treatment. In addition, since the particle size of the introduced pin follows the size of the added nanoparticle, the particle size of the pin can be easily and precisely controlled. Furthermore, since composition deviation does not occur when the oxide superconductor is formed, a desired high Jc or Ic oxide superconducting thin layer can be obtained. Among the above-mentioned materials, for example, a material having a high melting point such as Pt is prevented from moving and agglomerating or deforming in the calcining heat treatment and the main heat treatment forming the oxide superconductor. Therefore, it is more preferable.

Examples of the latter nanoparticles include nanoparticles such as CeO ₂ (cerium oxide), ZrO ₂ (zirconium dioxide), SiC (silicon carbide), TiN (titanium nitride), and the like. Reacts with the organometallic compound contained in the raw material solution, respectively, and BaNeO ₃ (barium cerate), BaZrO ₃ (barium zirconate), Y ₂ Si ₂ O ₇ , BaTiO ₃ (barium titanate), etc. It generates particles and functions as a magnetic flux pin.

  Since these nanoparticles generate pins by reacting with the organometallic compound contained in the raw material solution, they differ in composition from the nanoparticle that does not react with the above raw material solution when the oxide superconductor is formed. In view of this, it is preferable to prepare the raw material solution in advance.

The invention described in claim 2
2. The raw material solution for forming an oxide superconductor according to claim 1, wherein the nanoparticles have a particle size of 5 to 100 nm.

  If the particle size of the nanoparticles is too small, the function as a magnetic flux pin cannot be sufficiently exhibited. On the other hand, if the particle size is too large, the superconducting properties of the oxide superconducting thin film may be adversely affected.

  The particle size of 5 to 100 nm is a size corresponding to the coherence length, and there is no possibility that these problems occur.

The invention according to claim 3
3. The oxide according to claim 1, wherein an addition amount of the nanoparticles to the raw material solution is 0.01 to 10 mol% with respect to RE (rare earth element) in the raw material solution. This is a raw material solution for forming a superconductor.

  If the amount of nanoparticles added is too small, a sufficient amount of pins cannot be formed, and the function as a magnetic flux pin cannot be sufficiently exhibited. On the other hand, if the amount is too large, too many pins are formed, which may adversely affect the superconducting properties of the oxide superconducting thin film.

  When the amount of RE added to the raw material solution is 0.01 to 10 mol%, these problems do not occur.

The invention according to claim 4
The raw material solution for forming an oxide superconductor according to any one of claims 1 to 3, wherein a dispersant is added.

  Since the added nanoparticles may aggregate in the raw material solution, a raw material solution in which the nanoparticles are more uniformly dispersed can be prepared by adding a dispersant to suppress the occurrence of aggregation. .

  Specific examples of the dispersant include acrylic acid polymer, olefin-maleic acid copolymer, polyvinylpyrrolidone, polyethyleneimine, and the like. The addition amount is appropriately determined. When a commercially available nanoparticle dispersion solution or nanocolloid solution is used, the type of dispersant contained may not be disclosed, but there is no problem. In addition, it is preferable that these dispersing agents do not contain elements other than C, H, O, and N.

The invention described in claim 5
The raw material solution for forming an oxide superconductor according to any one of claims 1 to 4, wherein the organometallic compound is an organometallic compound containing no fluorine.

  When the above-described raw material solution for forming an oxide superconductor is applied to the FF-MOD method, the effect of the present invention can be remarkably exhibited. That is, unlike the case of using a raw material solution to which a conventional metal complex is added, it is easy to appropriately add to the raw material solution to appropriately control the formation of pins, and to sufficiently grow the orientation during crystal growth. Can do.

  The FF-MOD method using a raw material solution made of an organometallic compound not containing fluorine is different from the case of using the TFA-MOD method in forming an oxide superconductor layer, which is dangerous like hydrogen fluoride gas. No gas is generated, and no processing equipment is required.

  ADVANTAGE OF THE INVENTION According to this invention, the raw material solution which can control the particle size of a pin suitably can be provided, and the nanoparticle fully functioning as a magnetic flux pin is appropriately controlled by using such a raw material solution. Thus, the introduced oxide superconducting layer can be obtained, and an oxide superconducting thin film wire with improved Jc and Ic can be provided.

1 is a schematic cross-sectional view of an oxide superconducting wire created in Example 1. FIG. 5 is a schematic cross-sectional view of an oxide superconducting wire created in Comparative Example 1. FIG.

  The present invention will be described below with reference to the drawings based on the embodiments.

1. Production of Raw Material Solution First, a general production method of the raw material solution of the present invention will be described. In the following, Y is used as RE.

(1) Preparation of MOD Solution Starting from an organometallic compound of Y, Ba, and Cu, synthesis was performed at a ratio (molar ratio) of Y: Ba: Cu = 1: 2: 3 to prepare a MOD solution using alcohol as a solvent. To do. The total cation concentration of Y ³⁺ , Ba ²⁺ and Cu ²⁺ in the MOD solution is 1 mol / L.

  The organometallic compound includes an organometallic compound containing fluorine such as trifluoroacetate in the case of the TFA-MOD method, and fluorine such as acetylacetonate in the case of the FF-MOD method. Use no organometallic compound.

(2) Production of nanoparticle dispersion Separately from the production of the MOD solution described above, a predetermined amount of nanoparticles are dispersed in alcohol to produce a nanoparticle dispersion. At this time, a dispersant is added in order to prevent aggregation of the nanoparticles.

(3) Production of raw material solution Using the MOD solution and the nanoparticle dispersion produced as described above, mixing is performed so that the amount of nanoparticles added to Y is a predetermined mol%, thereby producing a raw material solution.

2. Formation of Y123 Oxide Superconducting Layer Next, formation of the Y123 oxide superconducting layer using the raw material solution prepared above will be described.

(1) Preparation of substrate First, a substrate on which an oxide superconducting layer is formed is prepared. As the substrate, Ni-W alloy substrate, a metal substrate of the clad type was an SUS or the like base metals, on such IBAD _substrate, an intermediate three-layer structure formed in the order of CeO ₂ / YSZ / CeO 2 An oriented metal substrate on which a layer is formed is preferably used.

(2) Application of raw material solution A predetermined amount of the raw material solution is applied on the substrate, and then dried to form a coating film having a predetermined thickness.

(3) Preparation of calcination film The said coating film is heat-processed on predetermined calcination heat treatment conditions, and a calcination film is produced.

(4) Production of main-fired film (oxide superconducting layer) The calcined film is heat-treated under predetermined main-heat treatment conditions to produce an oxide superconducting layer. At this time, a pin made of nanoparticles is formed in the oxide superconducting layer along with the formation of the oxide superconducting layer.

  Since the formed pin functions sufficiently as a magnetic flux pin in the oxide superconducting layer, an oxide superconducting thin film wire with improved Jc and Ic can be obtained.

  In this example, a raw material solution was prepared using Pt nanoparticles as nanoparticles, and a Y123-based oxide superconducting layer was formed using this raw material solution.

Example 1
1. Preparation of raw material solution (1) Preparation of MOD solution Each acetylacetonate complex of Y, Ba and Cu was prepared so that the molar ratio of Y: Ba: Cu was 1: 2: 3 and dissolved in alcohol. An alcohol solution of an organometallic compound was prepared.

(2) Pt nanoparticle dispersion platinum platinum colloidal solution (particle size: 10 nm, Pt concentration: 1 wt.%, Solvent: ethanol, dispersant does not contain elements other than C, H, O, N) .

(3) Preparation of raw material solution The alcohol solution of the prepared organometallic compound and the Pt nanoparticle dispersion are mixed so that the ratio of Pt to Y (Pt / Y) is 0.06 mol%. A raw material solution was prepared.

2. Formation of oxide superconducting layer (1) Coating film forming step and calcining heat treatment step Intermediate comprising three layers of Y ₂ O ₃ , YSZ and CeO ₂ on a clad substrate on which a Cu layer and a Ni layer are formed on SUS On the substrate provided with the layer, the prepared raw material solution was applied to form a coating film having a predetermined thickness. Thereafter, the temperature was raised to 500 ° C. in an air atmosphere, maintained for 2 hours, and then cooled to form a first calcined film having a thickness of 300 nm. Next, a second layer and a third layer were formed under the same conditions as the first layer to prepare a three-layer type calcined film.

(2) Main firing heat treatment step The obtained calcined film was heated to 800 ° C. in an argon / oxygen mixed gas atmosphere having an oxygen concentration of 100 ppm, held for 90 minutes, and then cooled to 500 ° C. in about 3 hours. Then, the atmosphere was switched to 100% oxygen, and the mixture was further cooled to room temperature over 5 hours to produce an oxide superconducting wire of Example 1 in which a Y123 oxide superconducting layer having a thickness of 0.75 μm was formed.

(Comparative example)
An oxide superconducting wire of a comparative example was produced in the same manner as in Example 1 except that a MOD solution not added with a dispersion of Pt nanoparticles was used as the raw material solution.

3. Evaluation of Oxide Superconducting Wire The oxide superconducting wire obtained in Example 1 and Comparative Example 1 was evaluated as follows.

(1) Cross-sectional structure Using the method of S-TEM, the cross section of the oxide superconducting layer formed in the oxide superconducting wire of Example 1 and the comparative example was observed.

  The observation results are schematically shown in FIGS. 1 is a schematic cross-sectional view of an oxide superconducting wire prepared in Example 1 and FIG. 2 in a comparative example. 1 and 2, 1 is a substrate, 2 is a formed Y123 oxide superconducting layer, and 3 is Pt nanoparticles.

  As shown in FIG. 1, in Example 1, it was confirmed that the Pt nanoparticles 3 were uniformly dispersed in the Y123 oxide superconducting layer 2. On the other hand, as shown in FIG. 2, formation of nanoparticles in the Y123 oxide superconducting layer 2 was not observed in the comparative example.

(2) Measurement of Ic The superconducting properties (Jc, Ic) of Example 1 and the comparative example were measured at 77K under a self magnetic field. The measurement results are shown in Table 1.

  From Table 1, by using the raw material solution to which nanoparticles were added (Example 1), a pin was formed in the oxide superconducting layer, and this pin functions sufficiently as a magnetic flux pin, so that Jc and Ic were improved. You can see that

(Examples 2 to 4)
The oxide superconducting wires of Examples 2 to 4 were obtained in the same manner as in Example 1 except that Pt nanoparticles having the particle sizes shown in Table 2 were used as the Pt nanoparticles.

  The superconducting properties (Jc, Ic) of the oxide superconducting wires obtained in Examples 2 to 4 were measured in the same manner as in Example 1. The measurement results are shown in Table 2 together with the results of Example 1.

3. Evaluation results The evaluation results of Examples 2 to 4 are shown together with the evaluation results of Example 1 in Table 2.

  From Table 2, it can be seen that in Example 3 and Example 1, a higher Ic was obtained than in Example 2 and Example 4. Such a result was obtained because in Example 3 and Example 1, the Pt nanoparticles had a particle size of 5 to 100 nm, and the function of the magnetic flux pinning point was further enhanced. .

(Examples 6 to 9)
1. Preparation of raw material solution The oxides of Examples 5 to 8 were prepared in the same manner as in Example 1 except that the ratio of Pt to Y (Pt / Y) contained in the raw material solution was changed to the mol% shown in Table 3. A superconducting wire was obtained.

  The superconducting properties (Jc, Ic) of the oxide superconducting wires obtained in Examples 5 to 8 were measured in the same manner as in Example 1. The measurement results are shown in Table 3 together with the results of Example 1.

  From Table 3, it can be seen that in Example 6, Example 1, and Example 7, a higher Ic was obtained than in Example 5 and Example 8. This result was obtained because in Example 6, Example 1 and Example 7, the moles of Pt and Y were 0.01 to 10, so that the function of the magnetic flux pinning point was further enhanced. It is because it has been.

Having described an example of using the Pt nanoparticles as _{nanoparticles, Ag, Au, BaCeO 3,} CeO 2, SrTiO 3, nanoparticles such as ZrO ₂ also has a similar flux pinning features and Pt nanoparticles It was confirmed that As described above, according to the present invention, an oxide superconducting layer having a higher Ic can be formed.

  As mentioned above, although this invention was demonstrated based on embodiment, this invention is not limited to said embodiment. Various modifications can be made to the above-described embodiment within the same and equivalent scope as the present invention.

1 Substrate 2 Y123 oxide superconducting layer 3 Pt nanoparticles

Claims (5)

A raw material solution for forming an oxide superconductor for forming an RE123-based oxide superconductor in which a magnetic flux pinning point is introduced on a substrate using a coating pyrolysis method,
A raw material for forming an oxide superconductor, wherein a predetermined amount of nanoparticles for forming the pinning point are dispersed in a solution in which an organometallic compound for forming the oxide superconductor is dissolved. solution.   The raw material solution for forming an oxide superconductor according to claim 1, wherein the nanoparticles have a particle size of 5 to 100 nm.   3. The oxide according to claim 1, wherein an addition amount of the nanoparticles to the raw material solution is 0.01 to 10 mol% with respect to RE (rare earth element) in the raw material solution. Raw material solution for superconductor formation.   The raw material solution for forming an oxide superconductor according to any one of claims 1 to 3, wherein a dispersant is added.   5. The raw material solution for forming an oxide superconductor according to claim 1, wherein the organometallic compound is an organometallic compound containing no fluorine.

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